An international team of researchers has succeeded in understanding, for the first time, how the topological properties of multilayer systems of Tungsten di-telluride (WTe2) can be changed systematically by means of scanning tunneling microscopy.
WTe2 has been found to be a promising material for the realization of topological states, which are regarded as the key to novel spintronics devices and quantum computers of the future due to their unique electronic properties.
Research on topological insulators is still quite nascent, and many fundamental questions remain unanswered. One of the distinguishing features of the compound WTe2 is that it exhibits a whole range of exotic physical phenomena depending on its layer thickness. Atomically thin layers are insulating on the surface, but due to their crystal structure they exhibit so-called topologically protected edge channels. These edge channels are electrically conductive and the conduction depends on the spin of the electrons. If two such layers are stacked on top of each other, crucially different interactions occur depending on how the layers are aligned.
If the two layers are not aligned, the conductive edge channels in the two layers interact only minimally. However, if they are twisted by exactly 180°, the topological protection as well as the edge channels disappear and the entire system becomes insulating. Furthermore, with a minimal twist of only a few degrees, a periodic superstructure, a so-called moiré lattice, forms, which additionally modulates the electrical conductivity. The researchers have now been able to study these properties locally on the atomic scale for the first time using a scanning tunneling microscope giving crucial insights into the interactions between the layers.